The present invention relates to an electronic circuit breaker for interrupting an electric power supply to a load when the current exceeds a pre-set value, for instance in the case of a short circuit.
There currently exist various types of circuit breakers for protecting circuits from over-currents. Some of these circuit breakers are of a thermal type and are based on the use of bimetallic strips, the deformation of which, on account of the dissipation of heat by the Joule effect due to the passage of current, causes opening of the circuit by a switch. In other circuit breakers, those of the electromagnetic type, interruption is caused by the movement of an armature under the effect of a magnetic field generated by a coil traversed by the current. In either case, an excessive current flowing through the strip (in the case of a thermal circuit breaker) or through the coil (in the case of a magnetic circuit breaker) causes tripping of the circuit breaker.
Thermal circuit breakers present the drawback of having a high tripping time and of being considerably unreliable because of the effect that ambient-temperature variations can have on their operation even when appropriate measures are taken to offset the effect of these variations.
Magnetic circuit breakers can be built in such a way that they trip very fast, this being necessary for protecting present-day circuits that comprise solid-state components. However, their tripping speed is not altogether satisfactory. In addition, their reliability is low in that they feel the effects of external ambient conditions, such as variations in temperature, mechanical vibrations, magnetic interference, etc. In addition, the presence of a mobile armature sets limits to the freedom of choice of the position in which these circuit breakers can be installed, on account of the influence that the force of gravity may have on the tripping characteristics of these devices.
There also exist electronic circuit breakers, for example of the type described in U.S. Pat. No. 4,979,068. Also these circuit breakers are not altogether satisfactory.